VDI 3786 Blatt 4:2012-04

The water vapour contained in the atmosphere is called air humidity. It plays an important part in the physical and chemical conversion of air pollutants. High humidity, for instance, favours the formation and growth of aerosols which cause a more frequent occurrence of haze and fog in polluted air, and, therefore, an alteration of the meteorological radiation budget. Due to precipitation, evaporation, and long-range transport of air masses, the water vapour content of the air varies considerably in different localities.In this Guideline hygrometric and psychrometric procedures are described by which the content of air humidity can be determined. Besides the measurement principles the installation, the calibration, registration, and the evaluation of the measured data are described. To provide comparability of the measurement results evaluation of data must be implied in measurement planning. The method of data collection, data transfer, and evaluation of data therefore is predestinated widely by the measurement task.